The innovations disclosed herein pertain to material processing systems, and more particularly, but not exclusively, to systems for producing elongate articles using extrusion techniques, such as, for example, powder metal and/or ceramic extrusion techniques. Some disclosed systems relate to producing an elongate article from a workpiece or from a material that undergoes a large strain during processing without fracturing the workpiece. Such materials can include compositions of feedstock including a mixture of a powdered bulk material and a binder system. Some disclosed systems pertain to continuous processing of materials, and more particularly, but not exclusively, to continuous processing of an elongate workpiece. Other disclosed systems pertain to products formed by processing an elongate workpiece from a material that undergoes large strains during processing.
Conventional powder processing systems, such as, for example, Metal Injection Molding (MIM) are not amenable to producing elongate articles for a number of reasons described below. Nonetheless, MIM techniques possess a number of advantages compared to conventional machining processes applied to wrought materials. For example, material properties arising from MIM techniques can approach those of wrought materials. Additionally, MIM techniques have been used to produce molded articles having intricate or complex shapes that traditionally have not been attainable by machining wrought materials. MIM techniques have also been used to produce net and near net molded articles having little dimensional variance (sometimes referred to as “close tolerances”), and to produce plural articles in one mold, thereby reducing production and/or assembly costs compared to traditional manufacturing techniques. MIM techniques have been used to produce molded articles for industries such as agricultural, automotive, business machine, electronics, food & beverage, hardware, medical, small appliance, and sporting goods.
A disadvantage to metal injection molding techniques has been their discrete nature, which limits a number of article units that can be produced in a given batch (or “press cycle”). Press cycle rate can be controlled in part by a time required to fill mold cavities with feedstock and to cool the resulting molded part sufficiently that it can be removed from the mold. Another disadvantage of metal injection molding is the difficulty in producing molded articles of substantial length in part because elongate articles formed using conventional MIM techniques fracture as they shrink during consolidation processes (e.g., debinding and sintering), in many instances. Yet another disadvantage of metal injection molding is the high cost of the molds which can produce only one particular molded part per mold cavity.
U.S. application Ser. No. 12/319,723, filed Jan. 12, 2009, published as U.S. Publication No. 2010/0178194 on Jul. 15, 2010, and assigned to the assignee of this application, discloses, among other things, systems pertaining to powder metal processing. For example, U.S. application Ser. No. 12/319,723 discloses methods that include extruding a mixture through a die to produce a green form, debinding the green form to produce a brown form, sintering the brown form to produce a densified form, and processing the densified form to produce an article. In some instances, such methods include receiving the green form on a setter tray and tilting the setter tray during debinding, thereby reducing the tendency of friction between the setter tray and the long form to cause a fracture in the form. U.S. application Ser. No. 12/319,723 is hereby incorporated by reference in its entirety, for all purposes.
U.S. Pat. No. 3,697,262, filed Jan. 15, 1971, discloses a method of handling shrinkable material. In particular, the '262 patent discloses conveying an elongated green metal component in a sinuous configuration through a furnace, enabling use of a short furnace. The '262 patent states “Importantly, the elongated component of sinuous configuration may lie in successively supported loops in a vertical plane . . . which allows for the progressive longitudinal shrinkage of the elongated green metal component . . . ” '262 patent, column 4, lines 18-27. The '262 patent discloses an elongated green metal component draped over a plurality of spaced apart pins 30. The spaced apart pins provide discrete locations of support to the green metal component, leaving portions of the green metal component spanning the gaps and hanging unsupported between adjacent pins. The unsupported and hanging portions of the green metal component constitute a vast majority of the component. Spaced apart ropes 26 pass through and are secured in the slotted ends of the pins 30, preventing the pins from rotating about a longitudinal axis of the pin. Thus, as the green metal component shrinks during processing, the internal stresses must overcome gravity and lift the weight of the unsupported portions, must overcome a static or sliding friction between the component and a corresponding pin, or both. Such support arrangements are unsuitable for processing some feedstock compositions since the internal stresses arising from such support configurations exceed a critical threshold (e.g., a yield stress, stress rupture strength, an ultimate stress) of such feedstock compositions, leading to defects (e.g., fractures, necking (e.g., a reduction in cross sectional area of an article), or unsuitable microstructures) in densified or finished articles.
Accordingly, there remains a need for systems capable of producing articles of virtually any length from materials that undergo large shrinking (or negative) strains during processing, such as powered bulk materials while keeping internal stresses below a critical threshold. For example, there remains a need for systems capable of producing a long article which may be cut or otherwise segmented to form articles having one or more selected lengths from such materials. A need also remains to produce one or more elongate articles at a higher rate than molded articles currently can be produced using MIM techniques. A need remains for a system capable of producing non-molded articles having any desired cross-sectional profile while avoiding or reducing a likelihood of a fracture or other defect occurring in the finished article using relatively low cost, flexible tooling. Such non-molded articles can include, for example, solid, hollow, and multi-lumen shapes. There also remains the need for systems capable of producing non-molded articles of net or near net shape while avoiding or reducing a likelihood of shrinkage-related defects in the finished article.